This research uses the techniques of auditory psychophysics with human subjects to examine two fundamental features of hearing. One has to do with spatial hearing. Sound localization outside the world of the laboratory must deal with stimuli that are spectrally complex, with multiple sources that may come from different directions, and with echoes of those sources that must not prevent the listener's knowledge of the actual source direction. Experiments with earphones will be used to model the workings of the binaural auditory system, especially "binaural adaptation", a process whereby the system relieves cognitive load by reducing the rate of input information beyond the stimulus' onset. A major focus of the work on binaural processing will be directed toward acquiring better knowledge of spatial hearing in the complex real world. This technique employs a controlled environment which allows study of the effects of a large number of stimulus configurations. The environment is housed in an anechoic chamber, using the computer to simulate "sources" and "echoes" through multiple loudspeakers. In addition, it includes a large scale projection television system which allows study of the effects of visual cues on sound localization. A parallel thrust of this grant focusses on study of the rules and limitations of auditory attention. It seeks to understand the nature of attentional selectivity along various acoustic dimensions, including space, frequency, pitch and timbre, and to describe how multiple tokens along one or more dimensions can sometimes be fused to create the perception of auditory objects.